Reactions of arenes Flashcards
All reactions of arenes
Combustion
Bromine
Mixture of concentrated sulfuric +nitric acid
Halogenoalkanes and acyl chlorides
Combustion in oxygen of benzene
Produces carbon dioxide and water
Incomplete combustion of arenes produces?
A sooty flame
Containing unburnt carbon and carbon monoxide
Examples of electrophilic substitution
Halogenation (bromine + benzene)
Nitration (mixture of conc sulfuric and nitric acid + benzene)
Friedel crafts reaction (haloalkane/ acyl chloride + benzene)
Steps of electrophilic addition mechanism
Curly arrow from delocalised ring of electrons to electrophile
Then: Delocalised ring broken around 1 carbon (has a + inside) and this carbon is bonded to a hydrogen and electrophile now
Then: hydrogen bonded to carbon donates electrons to centre of benzene
Product: benzene with electrophile + a hydrogen ion
what must be ensured when the ring of delocalised electrons breaks around a carbon?
The ring doesn’t extend around past the points of the other carbon in the ring
Bromine + benzene is also known as?
Halogenation
Products of benzene bromination
Bromobenzene
Hydrogen bromine
What is the mechanism for bromination of benzene?
Electrophilic substitution
How is bromination of benzene electrophilic substitution?
A hydrogen on the benzene ring is substituted by a Br atom
Br+ acts as electrophile
Catalyst needed for bromination of benzene
Halogen carrier catalyst
EG FeBr3 or AlBr3
What temperature does bromination of benzene occur at?
Room temperature
Why is a halogen carrier catalyst required for electrophilic substitution of bromination of benzene?
To polarise the Br2 to produce a Br+ electrophile
bromination of benzene equation for polarisation of Br2 by catalyst
Br2 + FeBr3 → Br+ + FeBr4-
Electrophile used in bromination of benzene?
Br+
Regeneration of catalyst in bromination of benzene
H+ + FeBr4- → HBr + FeBr3
Overall equation for benzene bromination
C₆H₆ + Br₂ —–> C₆H₅Br + HBr
(catalyst cancels out)
Bromo benzene formula
C₆H₅Br
Can halogenation of benzene occur with other halogens?
Yes but the catalyst used must have the same halogen eg FeCl3 for chlorination, like FeBr3 for bromination
Benzene + nitric acid is known as?
Nitration
Products of benzene nitration
Nitrobenzene (Benzene with NO2 that substituted hydrogen)
Water
Nitrobenzene formula
C₆H₅NO₂
What is the mechanism for nitration of benzene?
Electrophilic substitution
How is benzene nitration electrophilic substitution?
Electrophile used = NO₂+
Substitutes a hydrogen on benzene = nitrobenzene
Catalyst used for nitration of benzene
Concentrated sulfuric acid
How does concentrated sulfuric acid act as a catalyst in nitration of benzene?
Generates the NO₂+ catalyst
Generation of NO₂+ electrophile from catalyst
2H₂SO₄ + HNO₃ ——> NO₂⁺ + H₃O⁺ + H₂SO₄⁻
Reformation of catalyst in nitration of benzene
H+ + HSO4- → H2SO4
H+ is what was substituted from benzene
Nitrating mixture
1 mole concentrated nitric acid to 1 mole concentrated sulfuric acid
Overall equation for nitration of benzene
C6H6 + HNO3 → C6H5NO2 + H2O
2 Friedel-Crafts reactions
Alkylation
Acyltation
What is alkylation?
Substitution of 1 hydrogen with alkyl group to benzene by adding haloalkane
IN ORDER TO ADD THE ALKYL GROUP FROM HALOALKANE TO BENZENE
Does alkylation add the halogen from haloalkane to benzene?
NO
To do that: halogenation of benzene using halide pos ion as electrophile
Catalyst needed for alkylation of benzene
Halogen carrier catalyst eg AlCl3 or FeCl3 (of any halogen)
Generation of electrophile in alkylation from halogen carrier catalyst
R-Cl + AlCl3 → R+ + AlCl4-
(can be any halogen)
What is the electrophile in alkylation?
alkyl cation
eg CH3CH2+
Reformation of halogen carrier catalyst in alkylation
AlCl4- + H+ → AlCl3 + HCl
Overall equation for alkylation of benzene
C₆H₆ + RX —–> C₆H₅R + HX
What is acylation?
Substitution of hydrogen on benzene with an acetyl group by addition of acyl chloride
Is the chlorine from acyl chloride added to benzene?
NO
Just the acetyl group which is O=C-R
Where R is the length of the acyl chloride
The carbon bonds to benzene using bond that was bonded to halogen
Acetyl group
O=C-R
catalyst needed for acylation of benzene
Halogen carrier catalyst
FeCl3 AlCl3
Electrophile in acylation
O=C-R+
